A mulitilayered ceramic wiring circuit board includes a plurality of ceramic insulating substrate layers laminated integrally, conductor layers with predetermined patterns supported on the respective ceramic insulating substrate layers and via hole conductors provided at predetermined positions of the respective ceramic insulating substrate layers for interconnecting the respective predetermined patterned conductor layers to form a predetermined wiring circuit.
Simultaneous firing of the ceramic insulating substrate layers, the conductor layers, and the via hole conductors for completing the multilayered ceramic wiring circuit board, particularly one with a high density interconnection therein, often causes cracking in the ceramic insulating substrate layers due to the difference in thermal expansion coefficients between the ceramic insulating substrate layers and the conductor layers and the via hole conductors. Especially when alumina with a firing temperature 1500.degree.-1650.degree. C. is used as the ceramic insulating substrate layers and tungsten or molybdenum as the conductor layers and via hole conductors, whose firing temperature agrees with that of alumina, thus being applicable to the simultaneous firing, cracking is caused in the ceramic insulating substrate layers during the simultaneous firing by thermal stress due to the difference in thermal expansion coefficients, since the thermal expansion coefficients of alumina, tungsten and molybdenum are 75.times.10.sup.-7 /.degree.C., 45.times.10.sup.-7 /.degree.C. and 54.times.10.sup.-7 /.degree.C. respectively (at room temperature to 500.degree. C.).
Further, with the increasing tendency of speed-up and high density of integrated circuits such as LSI made of silicon, a method of mounting the silicon LSI directly on the multilayered ceramic wiring circuit board has recently come into use for purpose of heat dissipation and speed-up of semiconductor devices. This mounting method, however, gives rise to problems in that with the increase in size of the silicon LSI, the thermal stress at the junctures between the silicon LSI and the multilayered ceramic wiring circuit board, caused by a temperature change during the mounting of the silicon LSI on the multilayered ceramic wiring circuit board, increases. Alumina is generally used for the conventional multilayered ceramic wiring circuit board as explained above, and the thermal expansion coefficient of which is 75.times.10.sup.-7 /.degree.C. (at room temperature to 500.degree. C.), is more than two times that of silicon i.e. 35.times.10.sup.-7 /.degree.C. (at room temperature to 500.degree. C.). The thermal stress at the junctures between the silicon LSI and the alumina multilayered wiring circuit board caused by a temperature change during the direct mounting becomes large, which leads to degradation of reliability of the junctures.
Further the alumina multilayered wiring circuit board lowers the electrical signal propagation speed, because the dielectric constant of alumina is as large as 9.5 (at 1 MHZ).
U.S. Pat. No. 4,460,916 discloses ceramic insulating substrate layers for the multilayered ceramic wiring circuit board, essentially consisting of crystals of mullite and crystals of cordierite occupying the interstices between the crystals of mullite. Since the thermal expansion coefficient of mullite and cordierite are 42-45.times.10.sup.-7 /.degree.C. and 10-20.times.10.sup.-7 /.degree.C. respectively, the thermal expansion coefficient of the resultant ceramic insulating substrate layers is 38-39.times.10.sup.-7 /.degree.C. which is close to that of silicon i.e. 35.times.10.sup.-7 /.degree.C., so that the breaking of wires at the junctures between the silicon LSI and the multilayered ceramic wiring circuit board is prevented. However the temperature for the simultaneous firing of the ceramic insulating substrate layers and the conductor layers and the via hole conductors made of tungsten or molybdenum has to be controlled in the vicinity of 1500.degree. C., because the cordierite phase disappears above that temperature. However, the conductor layers and the via hole conductors are insufficiently fired at the temperature of 1500.degree. C. In addition, since the thermal expansion coefficients of tungsten and molybdenum are 45.times.10.sup.-7 /.degree.C. and 54.times.10.sup.-7 /.degree.C., respectively and the difference in thermal expansion coefficient between the ceramic insulating substrate layers and the conductive layers and the via hole conductors made of tungsten or molybdenum is large, cracking is generated during the simultaneous firing thereof as in the case of using alumina for the ceramic insulating substrate layers as mentioned above.
Furthermore, semiconductor components made of gallium arsenide have been widely used recently. The thermal expansion coefficient of the gallium arsenide semiconductor components is 65.times.10.sup.-7 /.degree.C. Therefore, the thermal expansion coefficient of the multilayered ceramic wiring circuit board is preferably between that of silicon i.e. 35.times.10.sup.-7 /.degree.C. and that of gallium arsenide i.e. 65.times.10.sup.-7 /.degree.C.